Particle component analyzing apparatus, and equivalent particle diameter measuring method using same

ABSTRACT

A particle component analyzing apparatus and method using a microwave induced plasma to perform element analysis of particles, such as particles existing in a clean room; wherein an aspirator scans a filter to draw particles collected on the filter, and using the microwaves to excite the drawn particles to cause generation of an emission spectrum having a plurality of wavelengths indicative of the elements of the particle, which are measured by a plurality of monochrometers, and converted by an optoelectric converter into electrical signals to identify the different elements in the particle. The invention uses means for obtaining the cube roots of the outputs from the optoelectric converter. By obtaining the ratio of cube root outputs corresponding to the diameters of particles preprocessed into spherical shape of a reference element and of an element to be measured, and then by obtaining the cube root of an output from an element in a measurement sample and by multiplying it by the ratio of cube roots with respect to the reference element, there is obtained an equivalent particle diameter corrected for differences in sensitivity between the elements. Means are provided for determining the composition of a particle from the emission spectrum and for calculating the composition ratios of a plurality of elements from the different emission intensities.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates to a particle component analyzing apparatus whichuses a microwave induced plasma to perform element analysis of, forexample, particles which float in a clean room, and to a particlecomposition determining method for obtaining accurate equivalentparticle diameters from information obtained using such apparatus andfor determining the composition off the particles.

2. Description of the Prior Art

FIG. 1 shows a conventional particle component analyzing apparatus usinga microwave induced plasma. The apparatus comprises a disperser 1 havingtherein a filter 2, with solid particles to be measured (not shown inthe drawing) adhereto thereto, and an aspirator 3 which draws up solidparticles adhered to the filter 2, and feeds the particles through valve7c into one end of a discharge tube 4. Air is removed from insidedisperser 1 by a suction pump 5 and the He gas is introduced through aninlet 8 and valve 7b to maintain a pressure slightly higher thanatmospheric pressure. A carrier gas (e.g. He) is applied through inlet 9and valve 7a.

A microwave source 13 introduces microwaves into a cavity 17. Adetection window 16 is disposed at the other end of discharge tube 4. Anoptical window 17 is disposed facing detection window 16. A focusingunit 18 is provided comprising a concave mirror 18a and a reflector 18b.The emission spectrum caused by the microwave impinging on the particlesadhered to the filter causes the elements of the particles to emit anemission spectrum having a plurality of wavelengths. The emissionspectrum is guided through slit 19 after being reflected by reflector18b and then is guided into a signal processing section 20. Signalprocessing section 20 comprises four monochrometers 20b, each of whichreceives emission spectrum through one of four optical fibers 20c. Theoutputs of the monochrometers 20b are applied to central processing unit(CPU) 20a.

In the FIG. 1 apparatus, microwaves having a frequency of 2.45 GHz aregenerated by source 13 and are applied to cavity 14, and a plasma ofapproximately 4000° K. is created in discharge tube 4.

Solid particles guided into discharge tube 4 from dispenser 1 areatomized, ionized and excited in the plasma, and emitted as an emissionspectrum as they are reduced to their base states. This emissionspectrum is led out of discharge tube 4 in the axial direction thereof,then guided through optical window 17 into focusing unit 18, wherein theemission spectrum is focused, and then passed through slit 19, thenseparated into different wavelengths by monochrometers 20b, and thensignal processed by CPU 20a. In this manner, the elements contained inthe specimen particles are measured and displayed. Monochrometers 20bare provided with optoelectrical converters 20d, which output electricalsignals corresponding to the strength of light of the selectedwavelengths. Amplifiers 21, which are ordinary amplifiers, when FIG. 1is considered to show a prior art apparatus, amplify the output signalsfrom optoelectric converters 20d. The amplifiers 21 are disposed afterthe converters 20d. The sizes of the particles are classified accordingto the strength of the output signals from the amplifiers 21, such as,for example, three classes of large, medium and small.

It should be mentioned hereat that FIG. 1 shows amplifier 21 as being anordinary amplifier when the apparatus is a conventional apparatus. WhenFIG. 1 is illustrative of the invention, the amplifier 21 is a cube rootamplifier. The drawing distinctly shows that for the conventionalapparatus, an ordinary amplifier is used as amplifier 21, and that forthe illustrative embodiment of the invention, a cube root amplifier isused as amplifier 21, and FIG. 1 is to be understood be signify suchdual meaning.

Returning to FIG. 1, filter 2 has a predetermined surface area, andaspirator 3 scans the filter a plurality of times, for example, 15times, as shown in FIG. 2, and draws up the same quantity of particleseach time. It is assumed that the particles, including a plurality ofelements, are distributed throughout the filter surface, with theelements being present in the same proportions in each particle,according to the amounts present in the selected sample. That is to say,the elements drawn in by the multiple scans are assumed to be drawn upin the same proportion with each scan, and each monochometer is set toone wavelength to analyze one element during each scan. Elements ofwhich the emission spectrum wavelengths have been determined include,for example, Al, Fe, C, Si, Cu, B, K, Na, Ni, Cr, Ca, Cl, F, N, W, Ti,Mo, Mg, Zn, Au, Co, Mn, Pb, O, S, and Br.

Quality deterioration in semiconductor manufacturing, for example, iscaused by inaccurate measurement of the elements, that is composition ofan ingredient, and by inaccurate measurement of size or weight. Thus, bysimply analyzing the average quantity of an element would not besufficient to insure against quality deterioration.

SUMMARY OF THE INVENTION

The invention aims to resolve the foregoing and other problems anddeficiencies of the prior art.

An object of the invention is to provide a particle component analyzingapparatus and method for measuring equivalent particle diameters and fordetermining particle compositions using such apparatus, wherein byobtaining equivalent particle diameters of individual particles and byidentifying the compositions of the particles, extremely fine control isobtained, for example in the manufacture of semiconductors, and thelike.

The foregoing object is attained by the invention which encompasses aparticle component analyzing apparatus comprising an aspirator whichscans a filter and draws particles collected thereon and whereinmicrowaves are used to excite the particles and cause them to emit anemission spectrum having a plurality of different wavelengths which isthen guided to a plurality of monchrometers for measurement of thedifferent wavelengths, and converted into electrical signals usingoptoelectrical converters, whereby the plurality of elements in theparticles are identified. The particle component analyzing apparatus isprovided with means for obtaining the cube roots of the outputs from theoptoelectrical converters and by obtaining the ratio (e.g. R) of cuberoot outputs corresponding to the diameters of the particlespreprocessed into spherical form of a reference element (e.g. Si) as adenominator and of an element to be measured (e.g. Fe) as numerator.(Thus, R=Fe^(1/3) /Si^(1/3)), and then by obtaining the cube root of anoutput from an element in the measurement sample and by multiplying itby the ratio of cube root outputs with respect to the reference element,(e.g. Fe (measured) 1/3×R) an equivalent particle diameter is obtainedwhich is corrected for differences in sensitivity between the elements,and the composition of the particle is determined from the emissionspectrum of the elements contained in the particle, and the compositionratios of the plurality of elements are calculated from the emissionintensity. In the above ratio R, the cube root of the reference element(e.g. Si) can serve as the numerator instead of the denominator, inwhich case, the calculation will involve dividing of the cube root ofthe measured element by the ratio.

The cube root ratio R is obtained by a calculation means in the CPU fromelectrical signals taken on standard samples, which are commerciallyavailable, with any desired standard element, e.g. Si, being used as areference element and being the denominator of the ratio, and thestandard element to be measured, e.g. Fe, being the numerator of theratio. The diameter, e.g. 5 μm, of the element corresponds to a certainvoltage, as discussed in Step 3 of FIG. 3, given off by by converter20d. The signals are cube rooted in Step 4 of FIG. 3. The cube rootcalculation is by appropriate procedures in the computer of CPU, and isa well known procedure. The cube root is of signals which represent thediameters of the different elements. For example, in the standard sampleof the reference element Si, the diameter is 5 μm, as would be thediameter of the standard sample element to be measured Fe. Thecalculation of the cube root of the measured element multiplied by theratio R produces the resulting diameter of the measured element ascorrected.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram depicting a conventional apparatus. It is to benoted that when amplifier 21 is an ordinary amplifier, this apparatus isa conventional apparatus, and when amplifier 21 is a cube rootamplifier, then the apparatus is an illustrative embodiment of theinvention.

FIG. 2 is a view depicting how an aspirator scans a filter.

FIG. 3 is a flow chart depicting the procedure used in the analyzingmethod of the invention.

FIG. 4 is a view depicting an illustrative particle collecting apparatusof the invention.

FIG. 5 is an SEM photograph depicting particles adhered to the surfaceof a filter.

FIG. 6 is a graph depicting particle size distribution versus output ofan analyzing apparatus.

FIG. 7 is a view depicting a particle existing as a compound.

FIG. 8 is a view depicting two elements existing in one particle asmanifested in the outputs of four monochrometers.

FIG. 9 is a diagram depicting circuitry for converting the signals of anoptoelectric converter into digital signals using an Analog to Digitalconverter (A/D converter).

FIG. 10 is a flow chart depicting the process flow of the arrangement ofFIG. 9.

FIG. 11 is a view depicting an arrangement similar to FIG. 9.

FIG. 12 is a flow chart depicting a process flow for the arrangement ofFIG. 11.

FIG. 13 is a chart depicting the results obtained when themonochrometers were set to wavelengths of different elements for fourscans, and the numbers counted of the synchronized detected elements.

FIG. 14 is a graph depicting the relationship between the emissionintensity of Mg and the emission intensity of Si, based on the resultsof a scan in the range a of FIG. 13.

FIG. 15 is a graph depicting the relationship between the emissionintensity of Fe and the emission intensity of Si, based on the resultsof a scan in the range a of FIG. 13.

FIG. 16 is a graph depicting the relationship between the emissionintensity of Al and the emission intensity of Si, based on the resultsof a scan in the range a of FIG. 13.

FIG. 17 is a chart depicting the results obtained when themonochrometers were set to the wavelengths of different elements foreach scan and synchronized detected elements were counted.

FIG. 18 is a graph depicting the relationship between the emissionintensity of Na and the emission intensity of C, based on the results ofa scan in the range d of FIG. 17.

FIG. 19 is a graph depicting the relationship between the emissionintensity of Ca and the emission intensity of Si, based on the resultsof a scan in the range d of FIG. 17.

FIG. 20 is a graph depicting the relationship between the emissionintensity of Si and the emission intensity of C, based on the results ofa scan in the range d of FIG. 17.

FIG. 21 is a graph depicting the relationship between the emissionintensity of Ca and the emission intensity of C, based on the results ofa scan in the range d of FIG. 17.

FIG. 22 is a chart depicting the results obtained when, with a powder ofknown composition, the monochrometers were set to the wavelengths ofdifferent elements and synchronized detected elements were counted.

FIG. 23 is a chart depicting the relationship between the number ofsynchronized detected elements and the sizes of the elements for each ofthe three scans of the known powder of FIG. 22.

FIG. 24 is a graph depicting emission intensity ratios, with respect toC, of Si, N and S bonded to C, plotted on the vertical axis versusparticle diameter of C, plotted on the horizontal axis, based on theresults of FIG. 22.

FIG. 25 is a graph depicting changed emission intensity ratios, withrespect to C of Si, N and S, versus the particle diameter of C,resulting from changes to the conditions of the manufacturing process bywhich the known powder of FIG. 22 was produced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

As above mentioned, FIG. 1 also shows an illustrative embodiment of theinvention, when amplifier 21 is a cube root amplifier. The belowdiscussion of the invention apparatus and method using same will thusrefer to FIG. 1.

FIG. 3 shows the processing steps of the method of the invention, suchas used inside the central processing unit 20a of FIG. 1. The valuescalculated in steps 1 to 7 of FIG. 3, are stored in the memory, forexample, of the CPU, and analysis of measurement samples is carried outby performing steps 8 to 10. Also, in this preferred embodiment, lightemitted by monochrometers 20b are converted into electrical signals byoptoelectric converters and then processed in cube root amplifiers 21,A/D converted and inputted to the CPU. The embodiment involving fourmonochrometers will be described.

In Step 1, spherical elements are collected on a filter. The collectingapparatus used for this function can, for example, be of the kind shownin FIG. 4. In FIG. 4, a standard sample 30, of Si of a nominal particlediameter of, for example 5 μm is scattered over a table 31. Standardsamples of this kind are commercially available. An aspirator 3a, havinga suction inlet 32a, is disposed above table 31. The standard sample isdrawn in by suction inlet 32a being brought close to the surface oftable 31 and a gas (e.g. nitrogen, air, helium, etc.) being blownthrough the tube in the direction of arrow 32b to create reducedpressure at inlet 32a. A filter 2 is disposed at the outlet 32c ofaspirator 3a, and the standard sample 30 is caused to travel to and toadhere to the surface of filter 2.

FIG. 5 shows an SEM photograph of a number of Si particles adhered tothe surface of filter 2. The individual particles are separated fromeach other because of shock waves generated as the gas is injected intoaspirator 32. It can be seen from the photograph that although theparticles are of nominal diameter of 5 μm there is some variation intheir sizes.

In Step 2 of FIG. 3, an image analyzer (not shown in the drawings) isused to measure the particles using the SEM photograph. FIG. 6 shows theparticle size distribution of SiO₂ by percentages using hatched bars.The solid bars will be explained later in connection with step four.Particles of diameter 4.5 μm were the most numerous, at about 22%,followed by those of diameter 5 μm, constituting about 21%. It can beseen that in SiO₂, sold as being of a diameter of 5 μm, there is aparticle size variation of from 3.5 μm to 7.5 μm.

In Step 3 of FIG. 3, filter 2 is loaded into the analyzing apparatus ofFIG. 1, and in a plasma, the particles are atomized, and ionized andcaused to emit an emission spectrum. This light is converted intoelectrical signals corresponding to the sizes of the particles andoutputted by optoelectric converters 20d disposed in back ofmonochrometers 20b.

In this embodiment, aspirator 3 scans a predetermined area of filter 2in a predetermined time, for example, 4 minutes, and a number ofelectrical signals, corresponding to the number of particles drawn in,are outputted.

In Step 4 of FIG. 3, the electrical signals obtained in Step 3 areinputted into cube root amplifiers 21 of FIG. 1, which output the cuberoots of their inputs. The solid black bars of FIG. 6 show thepercentage variations in the outputs of the cube root amplifiers 21. Itcan be seen that this variation substantially corresponds to thedistribution of the particle sizes measured using the SEM photograph inStep 2.

In Step 5 of FIG. 3, outputs are specified for the particles based onthe distribution chart of FIG. 6. In experiments carried out by theinventors, the output of a cube root amplifier 21 for a 5 μm particlewas,for example, 2.5225 V. This value varies with the amplifier gain.

In Step 6 of FIG. 3, steps 1 to 5 are repeated for elements, such as,for example, Fe, Al, Cu, P in the form of particles of known size, forexample, 5 μm, (standard sample which is commercially available) and therelationship between the particle sizes and the corresponding outputsare found for each element. Even when the particle sizes are the same,their emission intensities differ depending on the element.

In Step 7 of FIG. 3, taking the emission intensity of, for example, Sias a reference, the ratios of the emission intensities of the elements,obtained in Step 6, are calculated. These values are stored in thememory of the CPU 20a, and are used as correction coefficients. Theratio is formed with the cube root of the standard reference element(e.g. Si) as the denominator and the cube root of the standard elementto be measured (e.g. Fe) as the numerator. That is R=Fe^(1/3) /Si^(1/3).The ratio R is multiplied with the cube root of the measured element Feto produce the equivalent diameter. That is, Fe(measured)^(1/3)×R=equivalent diameter of the measured Fe. Of course the ratio can beinverted (e.g. 1/R) and the cube root of the measured element divided bysuch inverted ratio. That is 1/R=Si^(1/3) /Fe^(1/3). Thus, the referenceelement can be in either the denominator or numerator, and, theresulting ratio is multiplied or divided whatever the case might be. Thecomputer in the CPU can just as easily do either.

In Step 8 of FIG. 3, a measurement sample containing the elements to bemeasured is prepared, for example, by drawing in air through a dustcollector in a clean room for a predetermined time and adheringparticles of collected dust to a filter.

In Step 9 of FIG. 3, a filter, with particles collected in Step 8thereon, is loaded into the analyzing apparatus and outputs of the cuberoot amplifiers 21 proportional to the emission intensities of theelements, contained in the measurement sample, are obtained.

Because in the case of this apparatus there are used four monchrometers,by severally adjusting the set wavelengths of the monochrometers,measurement of four elements at a time is carried out.

In step 10 of FIG. 3, the cube root amplifier output, obtained for eachelement, are corrected by being multiplied by the respective correctioncoefficients stored in a memory in step 7, and the equivalent particlesizes of each element are calculated. Advantageously in the invention,the cube roots are obtained of the outputs of the optoelectricconverters, so that the signals are compressed and their dynamic rangesare enlarged.

By the above process, the magnitudes of the volumes of the elements canbe obtained from the equivalent particle diameters.

There may be cases when the elements exist in the measurement sample inthe form of a compound. For example, if there is compound of Fe and Ni,such as shown in FIG. 7, assuming that the wavelengths for these twoelements are among the set wavelengths of the four monchrometers 2Ob,because the outputs of the compound are simultaneous, there will be Niand Fe emission spectrum at the same time, as shown in FIG. 8. In thiscase, also, because the amounts of emission spectrum, i.e. amounts ofthe outputs, differ according to the ratio of the elements in thecompound, it is possible to obtain equivalent diameters corresponding tothe ratio of the elements in the compound.

Although in the preferred embodiment, a case was discussed wherein thecube root amplifiers 21 are disposed as a stage after the optoelectricconverters 20d, and carry out analog processing, it is also possible asmeans of obtaining cube roots to convert the signals from theoptoelectric converters 20d into digital signals with an A/D converterand the carry out digital processing in a CPU. Any means, which obtainsthe cube roots of the outputs of the optoelectric converters 20dcorresponding to the elements and sizes of the particles, will suffice,and the invention should be so construed as not being limited.

FIG. 9 shows the circuitry, provided for each optoelectric converter21d, where output signals of converters 20d provided for eachmonochrometer 20b, are converted into digital signals by A/D converters53. In FIG. 9, the output of each converter 20d is inputted into, forexample, three amplifiers 50a,50b, 50c.

Peak hold circuits 51a,51b,5cc are disposed in back of amplifiers 50a,50b, 50c. A multiplexer 21 receives as inputs, the outputs of amplifiers502,50b,50c, and hold circuits 51a,51b,51c. An A/D converter 53 convertsthe output of multiplexer 52 into digital signals, which are applied viabus 55 to CPU 54.

A CPU 54 sets the amplifier gains of amplifiers 50a,50b,50c, resets peakhold circuits 51a,51b,51c, receives digital signals from A/D converter53 through bus 55, and performs data processing according to the desiredgain.

The output of CPU 54 is fed to a high level CPU 20a, where computationof cube roots determining diameters corresponding to the output signalof the optoelectric converters 20d is carried out.

FIG. 10 shows the process flow of the arrangement of FIG. 9. In Step 1,the gains of amplifiers 50a,50b, 50c are set to, for example, 0, 20 and40 dB, by CPU 54.

In Step 2 of FIG. 10, CPU 54 resets the hold values of the peak holdcircuits 51a, 51b, and 51c, and in Step 3, the CPU 54 judges whether ornot it is sample time. If the answer is YES, in Step 4, a channel, e.g.1, is selected to be inputted into multiplexer 52 according to apredetermined sequence. The resetting, sample time, and channelselection is performed according to a clock in CPU 54. In Step 3, if theanswer is NO, the sample time is again determined, until a YES isobtained.

The signal inputted into multiplexer 52 is converted into a digitalsignal by A/D converter 53 and sent through bus 55 to CPU 54. In Step 5,CPU 54 judges whether or not the signal is above a predetermined level.If the judgement in Step 5 is YES, then in Step 6a, CPU 54 carries outdata processing according to gain on the signal and transfers the signalto the high level CPU 20a in Step 10. If the judgement is NO in step 5,CPU does not perform data process of step 6a nor send the signal to CPU20a; instead, in Step 7, the CPU 54 commands the multiplexer 52 toreceive, in channel 2, the signal being held in peak hold circuit 51b.

The signal inputted into multiplexer 52 from peak hold circuit 51b,having been amplified 10 times (i.e. 20 dB) by amplifier 50b, isconverted into a digital signal by A/D converter 53 and sent through bus55 to CPU 54.

In Step 8, CPU judges whether or not the signal is above a predeterminedlevel. If the judgement is YES, then in Step 6b, data processing iscarried out according to gain on the signal and in Step 10 the signal istransferred to high level CPU 20a. If the judgement in Step 8 is NO, CPU54 does not process the data in step 6b nor send the signal to the CPU20a; rather, in Step 9, the CPU 54 commands multiplexer 52 to input inchannel 3, the signal being held in peak hold circuit 51c.

The channel 3 signal inputted to multiplexer 52 from peak hold circuit51c, having been amplified 100 times (i.e. 40 dB) by amplifier 50c, isconverted into a digital signal by A/D converter 53, and transmittedthrough bus 55 to CPU 54. In Step 6c, the CPU 54 carries out dataprocessing according to gain on the signal and transfers the signal inStep 10 to high level CPU 20a.

By the above process, it is possible, for example, to increase theoutput range from a range of 0 to 10 obtained when a single amplifier isused, to an expanded range of 0 to 1000. This increase in the dynamicrange is especially beneficial when particle sizes are expressed byequivalent diameters.

In the preferred embodiment, the case in which there are threeamplifiers, was discussed. However, two or four or more amplifiers maybe used. Also, if CPU 54 is made to select channel 1 of the multiplexerfirst, peak hold circuit 51a disposed in back of amplifier 50a, can bedispensed with. Also, CPU 54 and CPU 20a, can be one central processingunit performing both functions.

In the preferred embodiment, the gains of amplifiers 50a, 50b, 50c, wereset to 0, 20 and 40 dB, but the setup may be such that the gains areinstead 40, 20 and 0 dB, and CPU 54 judge whether or not the output ofamplifier 50a is saturated, and if it is saturated then select the holdvalue of amplifier 50b and judge whether or not that the latter issaturated, and again if amplifier 50b is saturated, the select the holdvalue of amplifier 50c.

FIG. 11 shows an arrangement wherein the outputs of amplifiers 50a, 50b,50c are directly inputted into A/D converters 53a,53b, 53c, and CPU 54sequentially directly reads out the outputs of A/D converters 53a, 53b,and 53c.

FIG. 12 is a diagram illustrating the process flow of the arrangement ofFIG. 11. In Step 1, the gains of amplifiers 50a, 50b, 50c are set to,for example, 0, 20 and 40 dB by CPU 54. Then, in Step 2, CPU 54 judgeswhether or not it is sample time. If the answer is YES, it goes to step3, and according to a predetermined sequence, in step 4, the output ofamplifier 50a is converted into a digital signal by A/D converter 53a,and sent through a bus 55 to CPU 54. If the answer is NO in Step 2, thesample time is again tested until the answer is YES. In Step 5, CPU 54judges whether or not this signal is above a predetermined level. If thejudgement is YES, then in step 6a, CPU 54 performs data processingaccording to gain on the signal, and transfers it to high level CPU 20a.If the judgement in Step 5 is NO, then CPU 54 does not process the datain Step 6a, nor send this signal to the high level CPU 20a; rather, inStep 7, CPU 54 inputs the signal from the A/D converter 53b, that hasbeen amplified 10 times (i.e. 20 dB) by amplifier 50b.

Then, in Step 8, CPU 54 judges whether or not that signal is above apredetermined level. If the judgement is YES, then in Step 6b, CPU 54performs data processing on the signal according to gain, and transfersthe signal to high level CPU 20a. In Step 8, if the judgement is NO,then CPU 54 does not perform data processing in Step 6b, nor send thesignal to high level CPU 20a; rather, CPU in step 9 inputs the signalfrom A/D converter 53c that has been amplified 100 times (i.e. 40 dB) byamplifier 50b, and in step 10 performs data processing on the signalaccording to gain and transfers the signal to high level CPU 20a.

With the above arrangement, and flow process, compared to thearrangement and flow process of FIGS. 9 and 10, because the signals donot pass through a multiplexer, the processing speed is correspondinglyincreased.

In the apparatus described, four monochrometers and four cube rootamplifers were used to simultaneously measure four different elements.However, because these devices have individual differences a differencein output occurs even when these devices measure elements of the samediameter at the same time. To resolve this problem, in the invention,the output of an arbitrary monochrometer is, for example made to be 1.With this as a reference, the outputs of the other monchrometers arestandardized, for example, to 0.9 and 1.1, etc. and the outputs of themonochrometers are corrected, based on those standardized values. Inthis way, it is possible to make the corrections to the outputs of themonchrometers.

Next, a method of determining the composition of a particle fromsynchronized detected elements contained therein, and a method forcomputing the composition ratios of a plurality of elements from theiremission intensities, will be described.

FIG. 13 shows the results obtained when airborne particles weredeposited on the surface of the filter of the apparatus described above,using a cyclone dust collector or the like, and the set wavelengths ofthe 4 monochrometers were set to the wavelengths of different elementseach time the aspirator scanned the filter; and the number ofsynchronized detected elements was counted. The vertical axis shows thenumber of synchronized detected elements counted. The horizontal axisshows what the synchronized detected elements were. The intervalslabeled a to d are four different scans in which the monochrometers wereset to the wavelengths of the four groups of elements a' to d',respectively.

That is to say, in the scan in range a, the monchrometers were set tothe wavelengths of elements Si, Mg, Fe and Al, and these elements weresynchronized detected approximately 50 times. Mg and Fe weresynchronized detected about 65 times. Synchronized detected elements ofother combinations are also shown. It can be seen that in the range a,the number of time Si, Fe and Al was synchronized detected was too smallto be shown in the graph.

In scanning range b, the monochrometers were set to the wavelengths ofthe elements Si, Na, Ca and Al, and in scanning range c themonochrometers were set to the wavelengths of elements S,P,Na and Ca.

Looking more closely at the results of the scanning during interval a,it can be seen that simultaneous emission spectrums of Si and Mg, and Siand Fe, were the most numerous.

FIGS. 14, 15 and 16 show the relationships between the emissionintensities, as measured in volts, of Mg, Fe and Al and those of Si,based on the measured results in range a shown in FIG. 13. FIG. 14 showsthe relationship between Si and Mg. FIG. 15 shows the relationshipbetween Si and Fe. FIG. 16 shows the relationship between Si and Al. Inthese graphs n is the number of emission spectrums in the scan. As canbe seen from the graphs, there are fixed correlations between theemission intensity of the elements, shown by straight lines A,B and C.That is to say, although the emission intensity varies with particlesize, if the emission intensity of one of the elements increases, thatof the other element also increases. This indicates that irrespective ofthe size of the particle, Si, Mg and Fe are present in fixed ratios.Thus, it can be inferred that the particles exist as compounds and thegradients of the straight lines A, B and C show the composition ratiosof the compounds. Using this index, it is possible to obtain detailedinformation on the compositions of the particles of matter.

FIG. 17 is a chart showing the results obtained when particles weresimilarly collected on a filter in a different atmosphere to that in thecase discussed above, and when the 4 monochrometers were set todifferent wavelength each time the aspirator scanned the filter, andwhen the number of synchronized detected elements (see horizontal axis)was counted (see vertical axis). Intervals a to d are four differentscans in which the monchrometers were set to the wavelengths of fourgroups of elements (a' to d') respectively. That is, in the scan of therange indicated by a, the monochrometers were set to the wavelengths ofelements Ni, Fe, Cr and Al, and all of these elements were synchronizeddetected a small number of times. Fe and Al were synchronized detectedabout 180 times. Also, there were a small number of synchronizeddetected elements in other combinations.

In the range of scanning indicated by interval b, the monochometers wereset to wavelengths of elements Si, Na, Cu and Cl. It can be seen thatthe number of times all of these elements were synchronized detected wastoo small to be shown on the chart, and that Si, Na and Cu weresynchronized detected about 110 times. In the scan in the range of d,the monochrometers were set to the wavelengths of Si, Na, Ca and C. Allof these elements were synchronized detected about 140 times. Na, Ca andC were synchronized detected about 150 times. Na and Ca weresynchronized detected about 170 times.

FIGS. 18 to 21 are graphs wherein are plotted the relationship betweenthe emission intensity (shown by volts) of elements C and Na (FIG. 18);Si and Ca (FIG. 19); C and Si (FIG. 20); and C and Ca (FIG. 21) in therange of d. It is not possible in any of the graphs to draw a straightline, like straight lines A,B, C shown in FIGS. 14 to 16. That is tosay, the emission intensity varies with particle size, but there is nocorrelation between when the emission intensity of one of the elementsincreases and when the other element emission intensity increases. Thismeans that these elements are present only as lumps and not ascompounds.

FIGS. 22 and 23 show results obtained when a functional materialconsisting of a mixed powder of a known composition (C, Si, N, S) wasanalyzed with the above described apparatus. FIG. 22 shows the number ofsynchronized detected elements (see vertical axis) and the elements (seehorizontal axis), in one scan. FIG. 23 shows the number of synchronizeddetected (see vertical axis) of each element (see horizontal axis) perscan, and the sizes of the elements expressed in particle diameters.Three scans were carried out. In all three scans, the element count andthe sizes were approximately the same, thus showing that the elementswere evenly distributed over the filter surface.

FIGS. 24 and 25 show the densities (i.e. proportion, by voltage ratio)of Si and N and S with respect to the particle diameter of C (i.e.voltage). The functional materials shown in FIGS. 24 and 25 wereproduced by different manufacturing processes. By making clear theserelationships between particle diameter and component density andfunctional material quality, it is possible to carry out quality controlin an effective and reliable manner. FIGS. 13 to 25 show resultscomputed by a CPU corresponding to CPU 20a of FIG. 1, as displayed on anCRT.

Advantageously, with the invention, in analyzing solid particles, byobtaining equivalent particle diameters of constituent elements and bydetermining what Kind of compound (i.e. compositions) particles exist,as, for example, semiconductor manufacturing and the like, extremelyfine control is made possible, and fine particle component analysis ofincreased dynamic range is made possible.

The foregoing description is illustrative of the principles of of theinvention. Numerous extensions and modifications thereof would beapparent to the worker skilled in the art. All such extensions andmodifications are to be considered to be within the spirit and scope ofthe invention.

What is claimed is:
 1. In a particle component analyzing apparatus fordetermining particle size and composition and comprising a filter onwhich particles are collected; an aspirator for drawing up the particlescollected on said filter; a microwave source for applying microwaves tosaid particles to cause said particles to be excited to emit emissionspectrum having a plurality of wavelengths; a plurality ofmonochrometers set to different wavelengths for measuring thewavelengths of said emission spectrum; and optoelectrical convertermeans for converting said emission spectrum to electrical signals foridentifying a plurality of elements in said particles; the improvementcomprisingmeans for obtaining cube roots of the electrical signals fromsaid optoelectric converter means, and for obtaining an equivalentparticle diameter corrected for differences in sensitivity between theplurality of elements by obtaining a ratio of cube roots of theelectrical signals from said optoelectric converter means correspondingto diameters of particles preprocessed into spherical shape of areference element serving as the denominator of the ratio and of anelement to be measured serving as the numerator of the ratio; and byobtaining a cube root of the electrical signal from said optoelectricconverter means corresponding to a diameter of an element to be measuredin a measurement sample and multiplying such obtained cube root by saidratio, thereby to produce said equivalent particle diameter of saidelement being measured.
 2. The apparatus of claim 1, wherein saidplurality of monochrometers have their outputs standardized by using anoutput from one of said monochrometer as a reference and with theoutputs being corrected based on the reference standard.
 3. A method formeasuring an equivalent particle diameter of a particle using a particlecomponent analyzing apparatus comprising a filter; an aspirator forscanning said filter to draw particles collected on said filter; amicrowave source for supplying microwaves to cause said particles tobecome excited and to emit emission spectrum having a plurality ofwavelengths; a plurality of monochrometers set to selected wavelengthsto measure the wavelengths of the emission spectrum; and optoelectricconverter means for converting the emission spectrum into electricalsignals to identify one or more elements in the particle and diametersthereof; and means for obtaining cube roots of the electrical signalsfrom said optoelectric converter means; wherein said method comprisesthe steps of:using a plurality of standard samples of known diameter andknown element, obtaining a ratio of cube roots of electrical signalsfrom said optoelectric converter means corresponding to diameters of areference element of said standard samples serving as the denominator ofthe ratio, and of an element to be measured of said standard samplesserving as the numerator of the ratio; using said analyzing apparatus,measuring a measurement sample containing at least one element to bemeasured and obtaining a cube root corresponding to the diameter of saidat least one element included in said measurement sample; andcalculating the product of the ratio and the cube root of the diameterof the at least one element obtained in the previous step, thereby toproduce an equivalent particle diameter of said at least one elementbeing measured.
 4. The method of claim 3, wherein said plurality ofmonochrometers are initially standardized by using the output of onemonochrometer as a reference, and correcting the outputs of theremaining monochrometers using such reference as the standard.